This invention relates generally to ink jet printing systems, and more particularly to piezoelectric ink jet printing systems.
A piezoelectric ink jet printhead is susceptible to problems when suddenly jarred. This is because the piezoelectric components of the printhead effect the delivery of ink to the orifices of the printhead at extremely low pressures. As a result, when the printhead is subjected to vibration or impact, the flow of ink through passages in the printhead and related supply lines may be interrupted, causing undesirable discontinuities in the supply of ink to the ink orifices and often necessitating xe2x80x9creprimingxe2x80x9d of the printhead. This problem is magnified when the line from the ink supply to the printhead is relatively long because there is a greater likelihood that vibration-induced shock moving through the line will disrupt the flow of ink. Previously, ink jet systems have used relatively small ink reservoirs located close to the printhead to reduce the length of the supply line. However, due to its small capacity, the reservoir must be refilled manually or replaced, at frequent intervals, which is inconvenient and increases downtime of the system.
Among the several objects of this invention may be noted the provision of an ink jet printing system having multiple printheads which can be independently located with respect to each other and with respect to a primary ink supply to allow greater flexibility in the use and application of the system; the provision of such a system which has multiple printhead assemblies each containing a secondary ink supply located adjacent to the printhead to reduce the length of an ink supply line, thus minimizing interruptions in ink flow due to vibration; the provision of such a system wherein the printhead and a secondary ink supply reservoir are contained within the same housing, and wherein the supply reservoir is adjustable to maintain a constant orientation for proper system operation when the printhead is rotated to print different size indicia; the provision of such a system which provides automatic refilling of a secondary ink supply to eliminate the need for frequent manual refilling; and the provision of such a system which includes a purge system for purging individual printheads and supply lines without overfilling the secondary ink supply.
Briefly, a piezoelectric ink jet printing system of this invention includes a primary ink supply and a plurality of piezoelectric ink jet printhead assemblies. Each assembly comprises a housing, a piezoelectric ink jet printhead in the housing, a secondary ink supply attached to the housing adjacent to the printhead, and an ink supply line for delivery of ink from the secondary ink supply to the printhead. The system further includes a pump for pumping ink from the primary ink supply to the secondary ink supply of each printhead assembly. Each printhead assembly is operable independently of the other printhead assemblies and is selectively movable with respect to the other printhead assemblies and with respect to the primary ink supply so that each printhead assembly can be positioned at a desired location without regard to where the other printhead assemblies are to be positioned and without regard to where the primary ink supply is positioned.
In a second aspect of this invention, the ink jet printing system includes a primary ink supply and a plurality of piezoelectric ink jet printhead assemblies. Each assembly includes a housing, a piezoelectric ink jet printhead in the housing, a secondary ink supply attached to the housing adjacent to the printhead, and an ink supply line for delivery of ink from the secondary ink supply to the printhead. The printhead of each printhead assembly includes a linear array of ink orifices through which ink is ejected to print indicia on a surface. Each printhead assembly further comprises a device for mounting the housing and printhead therein for rotation about a first axis extending generally perpendicular to the surface thereby to vary the height of the indicia printed on the surface by the printhead in the housing, and a device for locking the housing in a selected position of rotational adjustment according to the desired height of indicia to be printed. The secondary ink supply of each printhead assembly is rotatably mounted with respect to the housing of the assembly so that when the housing of the printhead assembly is rotated in one direction about said first axis, the secondary ink supply may be rotated in an opposite direction to maintain the secondary ink supply in a selected predetermined attitude.
In a third aspect of this invention the system comprises a primary ink supply and a plurality of piezoelectric ink jet printhead assemblies. Each assembly comprises a piezoelectric ink jet printhead, a secondary ink supply adjacent to the printhead, and an ink supply line for delivery of ink form the secondary ink supply to the printhead. The system further comprises a pump for pumping ink from the primary ink supply to the secondary ink supply of each printhead assembly and a purge system for each printhead assembly for delivering ink under pressure from the primary ink supply to the printhead of the assembly thereby to purge air from the printhead. The purge system comprises a purge line which bypasses the secondary ink supply of the printhead assembly to prevent the delivery of ink under pressure to the secondary ink supply during purging of the printhead.
Other objects and features will be in part apparent and in part pointed out hereinafter.